Production of aromatic thioethers



United States Patent ce 3,134,818 PRODUCTION OF AROMATIC THIOETHERSBasil S. Farah and Everett E. Gilbert, Morris Township,

Morris County, N.J., assignors to Allied Chemical Corporation, New York,N.Y., a corporation of New York No Drawing. Filed Jan. 29, 1962, Ser.No. 169,647 Claims. (Cl. 260-609) This invention relates to an improvedprocess for the production of aromatic thioethers. More specifically,the invention concerns the production of alkylmercaptophenols, andparticularly 4-alkylmercaptophenols, by reacting phenolic compounds withdialkyl disulfides in the presence of sulfonic acid catalysts.

Many phosphates and thiophosphates derived from alkylmercaptophenols areextremely potent insecticides. For example, the high insecticidalactivity of diethyl 4- methylmercaptophenyl phosphate derived from4-methylmercaptophenol is described by Fukuto and Metcalf in the Journalof Agricultural and Food Chemistry, volume 4 (1956), pages 930-935.

Commercialization of these phosphates and thiophosphates has beenhampered by lack of a simple and economical method of preparing theintermediate alkylmercaptophenols. The method now generally employed,With specific reference to the preparation of 4-methylmercaptophenol,involves starting with the highly expensive 4- aminophenol, convertingit to 4-mercaptopheno1 via the difficult and dangerous diazoniumreaction and then methylating the mercapto group. It has also beenproposed to prepare alkylmercaptophenols by reacting phenolic compoundswith dialkyl disulfides in the presence of catalysts, including aluminumchloride, aluminum bromide, ferric chloride, zinc chloride, tintetrachloride, antimony pentachloride, boron fluoride and bleachingearth. In order to obtain acceptable yields of alkylmer' captophenols,it is necessary to employ the catalyst in at least molecular amount withrespect to the dialkyl disul-.

fide. Moreover, in the reaction of phenolic compounds with dialkyldisulfides, the halide catalysts generally yield predominantly the2-isomers rather than the more desirable 4-alkylmercaptophenols.vantageous since it is abrasive to conventional processing equipment.Further, it is cumbersome to recover since it must be filtered andWashed with an organic solvent.

The primary object of the present invention is to provide an economicaland efficient process for the production of aromatic thioethers.

A more specific object is to provide an economical and efiicient processfor the production of alkylmercaptophenols, and particularly4-alkylmercaptophenols, by reacting phenolic compounds with dialkyldisulfides in the presence of sulfonic acid catalysts.

A still more specific object is to provide an economical and efficientprocess for the production of methylmercaptophenols, and particularly4-methylmercaptophenols, by reacting phenolic compounds with dirnethyldisulfide in the presence of sulfonic acid catalysts.

Other objects and advantages of the invention will appear hereinafter.

In accordance with the present invention, it has been found thataromatic thioethers may be produced in high yield by reacting anuclearly hydroxy-substituted aromatic compound containing at least onefree 2- or 4-position Bleaching earth is disad 3,134,818 Patented May26, 1964 with a dialkyl disulfide in the presence of a sulfonic acid ascatalyst, the mol ratio of the sulfonic acid to dialkyl disulfide beingnot more than about 0.25 to 1.

The nuclearly hydroxy-substituted aromatic compounds Which are preferredin the process of this invention are phenolic compounds selected fromthe group consisting of phenol and alkyl-substituted, aryl-substituted,halo-substituted and alkoxy-substituted phenols con taining a free4-position. Representative of these compounds are phenol,3-isopropylphenol, 3-tert.-butylphenol, S-methylphenol (3-cresol),3-ethylphenol, 3-methyl- 6-isopropylphenol, 3,5-diisopropylphenol,2,6-diisopropylphen01, Z-methyl-S-isopropylphenol,2,6-di-tert.-butylphenol, 3,5-dimethylphenol, Z-phenylphenol,3-chlorophenol and 3-methoxyphenol. Other suitable nuclearlyhydroxysubstituted aromatic compounds include 4-methylphenol (4-cresol),4-chlorophenol, l-naphthol and 2-naphthol.

The dialkyl disulfide employed in the process of the inventionpreferably contains alkyl groups having 1 to 5 carbon atoms. Among thesuitable dialkyl disulfides are dirnethyl disulfide, diethyl disulfide,di-n-butyl disulfide, di-i-butyl disulfide, di-n-amyl disulfide,di-i-amyl disulfide and di(chloromethyl) disulfide. Generally speaking,about 0.5 to 2.0 mols of disulfide per mol of aromatic compound areused, the preferred mol ratio being about 1 to 1.

The sulfonic acid catalyst may be employed in three forms: (1) as asulfonic acid per se such as methanesulfonic acid, benzenesulfonic acid,toluenesulfonic acid, ethanesulfonic acid, etc., (2) as a sulfonic acidformed by adding sulfuric acid to the nuclearly hydroxy-substitutedaromatic compound and (3) as an acid form ion-exchange resin such asDowex-SO (a sulfonated styrene-divinyl benzene copolymer having a totalexchange capacity ranging from 0.3 to 2.3). We prefer to use a sulfonicacid catalyst obtained by the addition of sulfuric acid to the nuclearlyhydroxy-substituted aromatic compound. Such catalyst is advantageousfrom the standpoint of economy and, in addition, has been found to giveparticularly outstanding results.

In order to attain high yields of aromatic thioethers, it is essentialto employ not more than about 0.25 mol of sulfonic acid catalyst per molof dialkyl disulfide. Preferably about 0.04 to 0.25 mol of sulfonic acidcatalyst per mol of dialkyl disulfide is utilized. When the catalyst isa sulfonic acid formed by the addition of sulfuric acid to the nuclearlyhydroxy-substituted aromatic compound, maximum yields are obtained usingabout 0.04 to 0.1 mol of catalyst per mol of disulfide.

The process of the invention is preferably carried out at the refluxingtemperature of the reaction mixture. Generally speaking, thistemperature is within the range of about to C.

In typical operation, the dialkyl disulfide is slowly added to arefluxed agitated mixture of the nuclearly hydroxysubstituted aromaticcompound and the sulfonic acid catalyst. The resulting mixture is thenvacuum distilled to recover the desired product. As preferred, aphenolic compound containing a free 4-position and the sulfonic acidcatalyst are mixed in a reaction vessel, and the mixture is heated torefluxing temperature. The dialkyl disulfide is then added slowly withstirring, e.g. over a period of about A to 4 hours. Refluxing takesplace steadily, and alkyl mercaptan is evolved as the reactionprogresses.

After addition of the dialkyl disulfide, the mixture is refluxed for anadditional period of about 1 to 4 hours and then vacuum distilled forproduct recovery.

The evolved alkyl mercaptan obtained as by-product addition of thedialkyl disulfide, i.e. dimethyl disulfidc, was begun. Refiuxingoccurred steadily, and methyl rncrcaptan was evolved as the reactionprogressed. After addition of the dimethyl disulfide, the mixture wasre- Of the invention Ca be mar t as $11011 $11106 it is all fiuxed foran additional period and then vacuum distilled. article of commerce, orit can be oxidlzed, e.g. with air, Wh h l was d as reactant,Z-methylmercapio- P q 'f phenol and 4-methylmercaptophenol wererecovered as The Present lnventlon is further illustrated by theproducts. In the case of the 3-methylphenol reactant, the amples S61forth below product was 3-methyl-4-methylmercaptophenol.

EXAMPLES 1 TO 9 10 The results of the examples are set forth in Table IThe following general procedure was followed in carry below.

Table 1 Conditions Z-methylmcreapto- 4-mcthylmercuptoproduct productAro- Exmatic M01 Disulfide M01 Catalyst Mel ample com- AddltionDigestion Per- 1 pound B.P., 0. cent B.P., 0. cent yield 1 yield 1 Hrs.C. Hrs. C.

1 PhenoL. 1.0 Dimcthyl. 1.0 Methane- 0.05 2 140-145 1 145-150 13 40sulionic acid. 2 do 1.0 -do 1.0 .do 0.08 2 140-145 1 145-150 105-110 at25 156-160 at 66 -25 mm -30 mm 3 .do...-. 1.0 .do 1.0 do 0.16 2 14311 1150 104-10821; 17 15 -1 0 1; 52

20-30 mm about mm. 4 d 1,0 1o 1.0 do 0.25 2 145-150 2 108-172 0 3 5 lo1.0 do 1.0 Bcnzene- 0.03 2 1605:! 1 100 102-105 at 28 146-150 atsuli'ionic 20 mm 10-15 mm 3.01 6 do 1.0 do 1.0 96% H250 0.04 2 130-135 2130-135 100-104 at 25 148-151 at (phenol- 10-15 mm 10-15 mm. sulfonicacid). 7 l 1.25 .do 1.0 do 0.25 4% 150-155 2 -170 13 61 8 2 do 1.0 lo0.8 Dovi'eX-50" 01 1% 153i1 2 153i1 103-106 at 18 153-150 at 74 (acidform). 25 mm 25 mm. 0 B-meth- 1.0 .do 1.0 Methane- 0.08 1 162-.E1 1.5102:1:1 0 224-228111; 70 ylsulfonic 1 atm. pheacid. n01.

1 Based on the aromatic compound consumed. 2 Reaction mixture washedbefore distillation. ing out these examples. The nuclearlyhydroXy-substi- EXAMPLES 10 TO 26 tilted 3101113119 Compound, P1131101 yp 1 In following Table II results of further experiments and i1165111101110 acid catalyst were mlXed 111 a reaction using the processdescribed in connection with Examples vessel equipped with a mechanicalstirrer, external heater, 1 t 9 are t f th I n f th examples, 0,04 ladditional funnel and reflux condenser. The mixture was 45 of 96% H 50was employed, and the reaction mixture heated to reflux, and, withcontinued stirring, dropwise was water-washed before vacuumdistillation.

Table 11 Conditions Product Ex- Aromatic Mols Disulfide Mols AdditionDigestion Product B.P., C. Percent sulfur amcompound plc Percent Hrs. 0.Hrs. 0. Calcu- Found Yield lated 10...- 3-isopropylphcnol. 0. 67Dimethyl--. 0.67 3 145-150 5 145-150 3-isopropyl-4- 145-150 at 17.6 17.897

mcthylmercap- 2-3 mm. tophenol. 11-... 3-et11ylphenol 1.0.. do 1 1.0 1150-130 4 130-150 3-cthyl-4-methyl- 133-134 at 10.0 18.0 100mercaptophenol. 2-3 mm. 12-... 3-rncthyl-6-iso- 1.0 do 1.0 1 150-130 4130-150 3-methyl-4-mcth- 130-132211; 10.3 10.2 00

propylphcnol. ylmcrcapto-G- 3-4 mm.

isopropylphcnol. 13".. 3,5-diisopropyl- 0.44 ...(10 0.44 3 150-160 0.5150-160 3,5-diiS0propyl-4- 154-157 at 14.2 14.5 80

phenol. methyhncrcap- 2-3 mm.

toplienol. 14---. 2-rnethyl-5-iso- 1.07 (10 1.67 1 150-130 4 130-1502-methyl-4-n1ctl1- 157-158 at 10.3 15.0 78

propylphenol. ylmcrenpt0-5- 12 mm.

isopropylphenol. 15-... 3,5-dimcthyl- 2.0 .....(10 2.0 1 150-130 4130-150 3,5-dimethyl-4- 155-160 at 10.0 10.3 00

phenol. rncthylmercap- 12 mm.

tophenol. 16.... 2-phenylpl1enol. 1.0 do 1.0 1 150-130 4 130-1502-phenyl-4-mcth- -200 at 14.8 14.7 77

ylmcrcapto- 15 mm. phenol. 17..-. 3-mcthowphenol" 0.5 .do 0.5 1 150-1304 -150 3-methoxy-4- 154-156 at 61 methylmcrcap- 4-5 mm. tophenol. 184-mcthylpl1enol... 2.0 do. 1.5 1 150-130 4 130-150 Z-methylmereap- -150at 74 to-4-methyl- 12 mm. phenol. 19.... 4-chlorophenol 2.0 do 2.0 1-130 4 130-150 2-methylmercap- 164-168 at 18.3 18.5 71

to-4-chloro- 15-20 mm. phenol.

See footnotes at end of table.

Conditions Product Ex- Aromatic Mols Disulfido Mols Addition DigestionProduct B.P.,O. Percent sulfur amcompound Percent ple Yleld Hrs. 0. Hrs.C. Oalcu- Found lated th 1. 1 150-130 6 130-150 4-methylmercap- 132lnaphthol 1 0 Dime yl 0 ap 21---- Phenol 2.0 Diethyl 1.6 1 160-170 2160-170 2-et l11ylfiercapto- 18 p en 4-ethylmercapto- 1 65 henol. 22.3-methylphenol 2.5 .do 0.82 3 160-165 3-methyl-4-e hyl- 42mercaptophenol. 23---- Phenol 3.4 Dl-n-butyL- 0.57 3 150-160 4-r iabl lgs r l l lercap- 36 P 24..-. do 3.2 Di-i-buty1 0.57 8 1604-1-butylmercap- 34 tophenol. 25.--. do 3.2 Di-n-amyl... 0.48 7 160-1704-n-amylmercap- 32 tophenol. 26 do 3.2 Di-i-amyl.-. 0.48 12 150-1554-i-amylmercap- 38 tophenol.

1 Based on the aromatic compound consumed. 2 Based on the disulfideconsumed.

While the above describes the preferred embodiments of our invention, itwill be understood that departures may be made therefrom within thescope of the specification and claims.

We claim:

1. A process for the production of aromatic thioethers which comprisesreacting a nuclearly hydroxy-substituted aromatic hydrocarbon compoundselected from the group consisting of phenol, alkyl-substituted,aryl-substituted, halo-substituted and alkoxy-substituted phenolscontaining at least one of a free 2-position and a free 4-position,l-naphthol and 2-naphthol with a dialkyl disulfide in the presence of asulfonic acid catalyst selected from the group consisting of 1)alkyl-substituted sulfonic acids, (2) aryl-substituted sulfonic acids,(3) sulfonic acids formed by adding sulfuric acid to the nuclearlyhydroxysubstituted aromatic hydrocarbon compounds and (4) sulfonic acidform ion-exchange resins, the mol ratio of sulfonic acid to disulfidebeing not more than about 0.25 to 1.

2. The process of claim 1 wherein the nuclearly hydroxy-substitutedaromatic hydrocarbon compound is phenol.

3. The process of claim 1 wherein the nuclearly hydroxy-substitutedaromatic hydrocarbon compound is an alkyl-substituted phenol containingat least one of a free 2-position and a free 4-position.

4. The process of claim 1 wherein the mol ratio of sulfonic acid todialkyl disulfide is about 0.04-0.25 to 1.

5. The process of claim 1 wherein the catalyst is a. sulfonic acidobtained by the addition of sulfuric acid to the nuclearlyhydroXy-substituted aromatic hydrocarbon compound.

6. The process of claim 5 wherein the mol ratio of sulfonic acid todialkyl disulfide is about 0.040.1 to 1.

7. The process of claim 6 wherein the nuclearly hydroxy-substitutedaromatic hydrocarbon compound is phenol and the dialkyl disulfidecontains alkyl groups having 1 to 5 carbon atoms.

8. The process of claim 6 wherein the nuclearly hydroxy-substitutedaromatic hydrocarbon compound is phenol and the dialkyl disulfide isdirnethyl disulfide.

9. The process of claim 8 carried out at the refluxing temperature ofthe reaction mixture.

10. The process of claim 9 wherein 4-methylmercaptophenol is recoveredfrom the resulting reaction mass.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR THE PRODUCTION OF AROMATIC THIOETHERS WHICH COMPRISESREACTING A NUCLEARLY HYDROXY-SUBSTITUTED AROMATIC HYDROCARBON COMPOUNDSELECTED FROM THE GROUP CONSISTING OF PHENOL, ALKYL-SUBSTITUTED,ARYL-SUBSTITUTED, HALO-SUBSTITUTED AND ALKOXY-SUBSTITUTED PHENOLSCONTAINING AT LEAST ONE OF A FREE 2-POSITION AND A FREE 4-POSITION,1-NAPHTHOL AND 2-NAPHTHOL WITH A DIALKYL DISULFIDE IN THE GROUPCONSISTING OF (1) ALKYL-SUBSTITUTED SULFONIC ACIDS, (2) ARYL-SUBSTITUTEDSULFONIC ACIDS, (3) SULFONIC ACIDS FORMED BY ADDING SULFURIC ACID TO THENUCLEARLY HYDROXLYSUBSTITUTED AROMATIC HYDROCARBON COMPOUNDS AND (4)SULFONIC ACID FORM ION-EXCHANGE RESINS, THE MOL RATIO OF SULFONIC ACIDTO DISULFIDE BEING NOT MORE THAN ABOUT 0.25 TO 1.